1. Field
The invention relates to a liquid crystal display (LCD) device and more particularly, to a method of forming a liquid crystal cell for a liquid crystal display device.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices have been spotlighted as a next generation display device having high value because of their low power consumption and good portability.
Optical anisotropy and the polarization characteristics of a liquid crystal material form the basis for driving an LCD device. Generally, an LCD device includes two substrates, which are spaced apart and face each other, and a liquid crystal layer interposed between the two substrates. Polarizers are disposed over outer surfaces of the two substrates, respectively. Each of the two substrates includes an electrode, and the electrodes of each substrate also face each other. Voltage applied to each electrode induces an electric field between the electrodes. Alignment of the liquid crystal molecules is changed by varying the intensity or direction of the electric field. The LCD device displays a picture by varying transmittance of the light according to the arrangement (or rearrangement) of the liquid crystal molecules.
An active matrix liquid crystal display (AMLCD) device, which includes thin film transistors as a switching element for a plurality of pixels, has widely used for flat television systems or monitors of portable computer systems due to its high resolution and fast moving images.
A related art LCD device will be described hereafter in detail with reference to figures.
FIG. 1 shows a schematic solid view illustrating a related art LCD device. In this LCD device, upper and lower substrates 10 and 30 are spaced apart from and face each other, and a liquid crystal layer 50 is interposed between the upper substrate 10 and the lower substrate 30.
A plurality of gate lines 32 and a plurality of data lines 34 are formed over the inner surface of the lower substrate 30 (i.e., the side facing the upper substrate 10). The gate and data lines 32 and 34 cross each other to define pixel regions P. A thin film transistor T serves as a switching element, and is formed at each crossing portion of the gate and data lines 32 and 34. An array of such thin film transistors T is arranged in a matrix form corresponding to crossings of gate and data lines 32 and 34. A pixel electrode 46, which is connected to the thin film transistor T, is formed in each pixel region P.
Although not shown in the figure, the thin film transistor T includes a gate electrode, a source electrode, a drain electrode, and a channel. A gate signal is applied to the gate electrode, and a data signal is applied to the source electrode. When the thin film transistor T turns on by the gate signal, the data signal is transmitted to the drain electrode from the source electrode through the channel.
The upper substrate 10 includes a color filter layer 12 and a common electrode 16 respectively formed on the inside (i.e., the side facing the lower substrate 30). Although not shown in detail in the figure, the color filter layer 12 includes three color filters of red (R), green (G), and blue (B) transmitting light in a specific wavelength range, and a black matrix blocks light in an area where liquid crystal molecules are not controlled. The black matrix is disposed between the color filters. Each color filter of the color filter layer 12 corresponds to the pixel electrode 46 at the pixel region P.
Upper and lower polarizers 52 and 54, each of which may be a linear polarizer that transmits only linearly polarized light parallel to its light transmission axis, are arranged over outer surfaces of the upper and lower substrates 10 and 30, respectively. Additionally, a backlight disposed over the outer surface of the lower polarizer 54 functions as a light source.
The LCD device may be fabricated through a liquid crystal (LC) cell process. The LC cell process includes interposing a liquid crystal material between two substrates, which have switching elements and pixel electrodes through a manufacturing process of an array substrate and color filters and a common electrode through a manufacturing process of a color filter substrate, respectively. The LC cell process may hardly include relatively repeated processes as compared with the array process and the color filter process. The LC cell process includes forming an alignment layer for aligning liquid crystal molecules, forming a cell gap, cell cutting, and injecting a liquid crystal material. A liquid crystal panel is manufactured through the above the LC cell process.
FIG. 2 is a schematic plan view illustrating a cell arrangement on a motherglass for an LC cell process according to the related art.
As shown in FIG. 2, a cell region IIA in which array elements 62 are formed is defined on a motherglass 60. The cell region IIA becomes a cell through a cutting process to be performed later.
Although not shown in the figure, the cell region IIA includes a first area in the middle portion and a second area at the edge of the first area. A region except for the cell region IIA corresponds to a dummy region IIB, which is thrown away after the cutting process.
The motherglass may correspond to a base substrate on which a plurality of cell regions may be defined. Although the base substrate is made of glass, the base substrate may be made of plastic.
The LCD device may be used for various display devices and may have various sizes of substrates. It is difficult to form motherglasses according to the size. Thus, according to circumstances, because the dummy region may increase in the motherglass, the material cost substantially increases accordingly.
To solve the above problem, a multi-model on glass (MMG) method has been proposed. To improve utilization of the dummy region of the motherglass, in the MMG method, a large size cell and small size cells are arranged on one motherglass.
FIG. 3 is a schematic plan view illustrating an LC cell arrangement in an MMG method according to the related art. In FIG. 3, a first cell region IIIA and two second cell regions IIIB are arranged on one motherglass 70 and spaced apart from each other. The first cell region IIIA has a first size and the second cell regions IIIB have a second size smaller than first size.
The structure of FIG. 3 improves the utilization efficiency of the dummy region as compared with a structure in which only one size substrate is arranged on the motherglass, and the material costs are reduced.
However, in the related art MMC method, a rubbing process is performed along a vertical direction R in the context of the figure, that is, a direction from the second cell regions IIIB to the first cell region IIIA. At this time, rubbing properties of the first cell region IIIA may be lowered due to a step in a portion between the second cell regions IIIB.
FIGS. 4A and 4B illustrate a rubbing process according to the related art. FIG. 4A is a cross-sectional view along the line IVA—IVA of FIG. 3 and FIG. 4B is a cross-sectional view along the line IVB—IVB of FIG. 3.
In FIG. 4A, a first cell region IIIA and a second cell region IIIB are spaced apart on a motherglass 70. A first array element 74 and a first alignment layer 76 are sequentially formed in the first cell region IIIA. A second array element 78 and a second alignment layer 80 are sequentially formed in the second cell region IIIB.
Although not shown in the figure, each of the first and second array elements 74 and 78 includes a gate line, a data line, a thin film transistor, and a pixel electrode. A color filter element may be formed in place of the array element.
The first and second alignment layers 76 and 80 are rubbed with a rubbing fabric 84, which has a plurality of pile yarns 82 at a surface thereof, to thereby form grooves (not shown) along a predetermined direction on the first and second alignment layers 76 and 80. Depths of the grooves depend on a force pressed by the rubbing fabric 84.
In FIG. 4B, the first cell region IIIA is disposed on the motherglass 70, and is rubbed with the same rubbing fabric 84 as that of FIG. 4A. At this time, since there is no cell region before the first cell region IIIA, the first cell region IIIA is directly rubbed by the rubbing fabric 84, which is not previously pressed in a portion corresponding to a space between the second cell regions IIB of FIG. 3. Thus, the first cell region IIIA of FIG. 4B is less pressed by the rubbing fabric 84 than the first cell region IIIA of FIG. 4A. Accordingly, arrangements of liquid crystal molecules differ in positions, to thereby lower an image quality.